A method and apparatus for regulating electric power being supplied to a polyphase synchronous machine under load is disclosed.
When supplying power to a polyphase synchronous machine that consumes a tremendous amount of electrical power, several needs compete and must be simultaneously considered in managing its electrical power distribution. A first concern has to do with maintaining delivered electrical power voltage levels within predetermined limits. A second concern relates improving overall efficiency of electrical power usage and distribution. A third concern relates to these and other concerns in light of changing electrical loading of the machine and variations in the character of the loading so that the voltages do not decrease to such a level that the synchronous machine enters a state known as pull-out, in which the stator and rotor magnetic fields fail to maintain mutual engagement, characterized by the rotor field slipping out of engagement with the rotating magnetic field of the stator. This condition, commonly known as either pull-out or pole slip, can result in damage to the machine. The mechanical load condition at which pull-out or pole slip occurs is known as the pull-out torque.
One technique to accommodate changes in electrical loading is to set preset threshold levels at high enough levels at which pull-out is not likely to occur. Although this technique provides a margin of safety for the machine, it results in inefficiencies as the voltage of the system must be kept sufficiently high at all times even when the machine is not under a high load. Thus for an energy efficiency standpoint, a lot of energy is wasted providing unnecessarily high margins of safety.